Rectifier efficiency?

[jjman]

Here what I have in a book. I loaded it into a xcel, then xml and then pdf to get it to load.

Mark

Mark, that's EXACTLY the info I'm looking for. THANKS SO MUCH!!!!!!!!!!!!!!!!!!!!!

David, I get what you're saying (I think), and my setup is a cathode biased pair of 6V6s that I'd like to run in Class A. I'm thinking I'll stick with a 270v PT for now and see if that gets me close....and I can always play with the cathode resistor if need be.

FYI, I'm using a 265-0-265 PT with diode rectification on 2 6v6s in cathode bias @ 12 watts each. Plates are 344 volts with 21v on the cathodes and about 37ma idle ea. 250ohm cathode resistor. Definitely not class A according to the scope. Pretty far from it.

Not sure if going to 14watts idle would reach class A using my setup.

[tonestack]

FYI, I'm using a 265-0-265 PT with diode rectification on 2 6v6s in cathode bias @ 12 watts each. Plates are 344 volts with 21v on the cathodes and about 37ma idle ea. 250ohm cathode resistor.

What is the current rating for your power transformer?

[tonestack]

I was using my old 1963 12th Ed. Sylvania Tecnical Manual I've had for so many years I can't remember.

So I also am posting this wedsite so that you can figure out the data you are looking for.

http://tdsl.duncanamps.com/show.php?des=5V4
http://tdsl.duncanamps.com/show.php?des=5Y3

You did not answer my question. You gave us voltage drops, but a voltage drop has to be with respect to some other voltage. How is the reference voltage calculated? If you say the square root of 2 x secondary AC voltage, then your data is incorrect. Tube rectifiers do not have fixed forward voltage drops. The closest that we can get to modeling their behavior without resorting to calculus is to use some kind of linear approximation, which only gets us into the ballpark.

As I stated earlier, the output of a 5Y3 can be approximated using the following equation along as the current draw is between 80 and 100ma and the power transformer is capable of delivering this much current without sagging:

DC ~= 1.1 x SAC, where SAC equals the power transformer's secondary AC voltage.

275 VDC ~= 1.1 x 250 VAC
330 VDC ~= 1.1 x 300 VAC

Now, if we were to rectify this secondary using Si diodes, we would achieve near lossless rectification between AC and DC.

(note: we will use 1.4 instead of the SQRT(2) to simplify matters here)

350 VDC ~= 1.4 x 250 VAC
420 VDC ~= 1.4 x 300 VAC

Now, the deltas between the two sets of numbers represent the loss that was experienced using the 5Y3.

350 VDC - 275 VDC = 75 volts
420 VDC - 330 VDC = 90 volts

As anyone can see, the voltage drop across a 5Y3 is not fixed like it is on a Si diode. On an Si diode, the forward voltage drop is 0.6V regardless of whether we are using a 250-0-250 power tranny or a 300-0-300 power tranny. The Si diode drop is so low that it can be thrown out of the equation when dealing with tube high-voltage tube power supplies.

[dehughes]

Cool. Thanks for the links and info, guys.

At this point, the only figures I need are the "average" voltage drop of a EZ81 (cannot seem to find it explicitly stated on the tube sheet, or able to deduce it from the info given) and the maximum input capacitance of a 5V4 and 5R4 (again, not explicit on the data sheets.

Maybe these values are staring me in the face, but I'm not seeing them.

[M Fowler]

Here is another one.

The Max voltage drop given corresponds to the load current given in column 3. If the rectifier is supplying less current the corresponding voltage drop across it will be less.

Per Tino Zottola

[jjman]

FYI, I'm using a 265-0-265 PT with diode rectification on 2 6v6s in cathode bias @ 12 watts each. Plates are 344 volts with 21v on the cathodes and about 37ma idle ea. 250ohm cathode resistor.

What is the current rating for your power transformer?

300ma. It's the Toneslut TWPT. Says 260-0-260 on the spec sheet but my line is higher than 120vac.

[Structo]

Yes, strange that the voltage drop is not a featured spec like other tube rectifiers show.

The closest I can come to an actual number is :
As a full wave rectifier True RMS voltages:

At 250 plates the output is 240v

At 300v output is 295v

And at 350v the output is 350v

All at 150ma.

http://www.r-type.org/pdfs/ez81.pdf

[tubeswell]

Hi de hughes

Everyone else has said their piece, and forgive me for being anal javascript:emoticon(':o'), but I use

SS = 1.4142

5AR4 = 1.31

5U4GB = 1.21

5Y3GT = 1.1

As a rough rule of thumb, in most geetar amps the B+ difference is about 30 V between each rectifier type listed above (with the 5Y3GT being the lowest and SS being the highest) and I might well get shot down in flames for saying that.

a 5V4 sits somewhere between a 5U4GB and a 5AR4

a 5R4 is between a 5Y3GT and a 5U4GB

For an EZ81, you ideally should have a separate 6V winding (instead of running it off the heater filament winding). Helps reduce noise.

As one of the other posters said - you only need the ballpark for the right reaction to occur.

Also FWIW some (coke-bottle) rectifiers identified as '5U4G' are not the same as a 5U4GB, but a Sovtek '5U4G' (coke bottle) is closer to a 5U4GB , having a maximum output of 250 mA (instead of 225mA for a 5U4G).

[dehughes]

Right on. Thanks guys!

[tubeswell]

I did a 5E3 last year with a 325-0-325 PT and a 255r cathode resistor bypassed with 22uF. With a 5Y3GT and 2 x 6V6s, it idled around 12-13W as I recall. I got about 365ish I think from memory (which I zenered down to about 350 with a 5W 15V zener on the HT CT). It sounded pretty sweet with a G12 20W. I think they sound better in Class A if you have lower plate voltages

With a 5AR4 and 2 x 6L6GC plugged in to the same amp I got 412 on the plates IRRC, and the 6L6 s were idling at around 70% (with the same cathode resistor - i.e.; straight plug-in). (Edit: Mind you the PT HT was 325-0-325 @ 180mA, and the Heater was 4mA, and the OT was 25W capable of either 4k or 8k primary Zed)

[dehughes]

Nice. Good info.

[aclempoppi]

Just a tech on the sidelines. Thought I knew a little about amps, now I see I know very little. Appreciate all of your info! ART

[dehughes]

Very cool! Thanks so much guys.....exactly the info I needed. Here is what I'm thinking I'll have Heyboer make for me:

PT with the mounting dimensions/style of the 125P17A (e.g., laydown mount, centers being 2 1/4" x 2 13/16").

Rating for AC 120v

Hi Volt: 270-0-270 @120ma

5V: rated @ 3A

6.3v: Center tapped (6.3-0-6.3), rated @ 5A

I figure this should be enough to comfortably run a 6V6 pair, a 5AR4 recto, two 12AX7s and one 6SN7, while keeping plate voltage for the cathode biased 6V6s (300 ohm Rk) in the 320-ish range (I like low-ish voltages, I've found...). Thoughts?

That transformer is going to put your in the 350 +/- 5VDC range with a 5AR4 rectifier. You will need to drop down to using a transformer with a 250-0-250 120ma secondary to hit 320VDC.

Alrighty. Come Tuesday I'm going to place an order with Heyboer for the above spec'd transformer, save for 250-0-250v primaries....all other ratings and specs will be as listed. Any suggestions? Anything I'm missing?

Thanks.

[dehughes]

...

[Mars Hall]

Reviving an old thread here. I'll be converting a Bassman LTD RI to original specs. The current PT's put out to much B+. Typically 470v - 480v. I've been considering a PT swap to get the voltages down to 440v 450v.

So. I should be looking for 340v x 1.3 = 442v, if I understand this thread correctly. Do I have this about right?

Anyone with experience in the 5F6-A type build? Please let me know how yours turned out. Thank You.